This invention relates generally to motorized operators for circuit breakers used on electrical power systems and the like and specifically to electrical operators for such mechanically operated circuit breakers that may be readily installed on site, i.e. in the field.
One of the principal advantages of having the capability of electrically opening and closing circuit breakers is the ability to remotely operate the breaker in response to operator control as well as in response to fault currents. With electrically controlled motorized systems for opening and closing the circuit breakers, load switching and branch circuit protection may be rapidly and effectively accomplished because of the elimination of the need for a technician to physically manipulate the operating mechanism of the circuit breaker.
In many instances, it is desirable to upgrade a mechanically operated breaker by installing a motor control system therefor. Most of the motor control systems include mechanical electric switches to run the bidirectional motor in addition to limit switches for stopping the motor when the breaker reaches an operating position, i.e. either fully opened or fully closed. It is desirable to open or close a breaker rapidly and the limit switches, especially, are difficult and awkward to adjust in the field, and may be adjusted improperly.
As alluded to above, it is desirable that the circuit breaker operate to open or close all electrical phases as rapidly as possible and within a minimum time period for all phases. The motor drive must therefore rapidly start the motor, deliver very high torque for approximately 105 degrees of angular rotation, and rapidly stop. These severe requirements have necessitated the use of expensive apparatus that requires careful adjustment.
The present invention is directed to a novel torque limited module that may be used to couple a bidirectional high torque motor to the operating mechanism of a multiphase circuit breaker through a single reduction gear. The torque limited module includes a clutch that is centered on a drive shaft and precisely loaded by means of a centering and spacing ring in the form of a cylinder. An upper and lower module plate embraces the spacer ring, which houses all of the clutch elements. A pair of Belleville washers load the clutch and a pair of friction discs, separated by a spacer ring, increases the clutch frictional force. The spacer serves to increase the surface area of friction slippage and improves the operation of the clutch. This torque limited module permits the motor to overrun the breaker operation, i.e. the motor runs for a short time after the breaker has been fully operated, that is opened or closed. The field installable electrical operator and the electronic motor control systems are individually the subjects of the above mentioned copending applications since they have separate utility apart from the present invention.